1. Field of the Invention
The invention relates to a labyrinth mechanism of a motor that is driven to rotate disklike rotating members. For example, the invention is applicable to a motor for driving disklike rotating members such as hard disks and polygon mirrors.
2. Related Art
FIG. 3 shows a conventional example of a disk drive motor. In FIG. 3, a frame 1 has a platelike bracket portion 3 and a center shaft 2 that is formed integrally with the bracket portion at the center of the bracket portion. Inner rings 5a, 6a of upper and lower ball bearings 5, 6 are fixedly fitted with the outer circumference of the center shaft 2. Outer rings 5b, 6b of the ball bearings 5, 6 are also fixedly fitted with an inner hole 13 of a hub 7, so that the hub 7 is supported so as to be rotatable about the center shaft 2.
An annular yoke 9 made of a magnetic material is fixed to a lower portion of the hub 7, and an annular drive magnet 8 is fixed to the inner circumferential surface of the yoke 9. Further, in a lower portion of the center shaft 2 is a core holding portion 4, which is integrally formed with the center shaft 2. A stator core 10 is fixedly fitted with the outer circumference of the core holding portion 4. The stator core 10 has a plurality of salient poles, each of which has a coil 11 wound around. The outer circumferential surface of each salient pole confronts the inner circumferential surface of the drive magnet 8 while interposing an appropriate distance therebetween.
The ball bearings 5, 6 have seal members 5c, 6c to prevent dust produced by the ball bearings 5, 6 from leaking outside the motor and being deposited on such signal reading means as the disk and the magnetic head to affect the functions of the signal reading means while the motor is rotating.
Further, a magnetic fluid seal mechanism serving as a first seal means 14 is not only arranged along the way to a space 19 outside the motor from the upper ball bearing 5 but also arranged so as to bridge between the top of the center shaft 2 and that of the hub 7 as viewed in FIG. 3. The first seal means 14 prevents dust such as oil mist from the ball bearings 5, 6 from scattering into the space 19 outside the motor and thereby depositing on a disk D and the like.
On the other hand, a small gap is provided along the way to the space 19 outside the motor from the lower ball bearing 6. The small gap is also interposed between the inner circumferential surface of the bracket portion 3 of the frame 1 and the outer circumferential surface of the yoke. This small gap constitutes a second seal means 24.
These first seal means 14 and second seal means 24 are known seal means and are provided to prevent the leaking of dust outside the motor, the dust being produced by the ball bearings 5, 6 arranged inside the motor.
The inner hole 13 of the hub 7 has a small diameter portion 17 whose diameter is smaller than the portion of the inner hole 13 which holds the ball bearings 5, 6. The outer rings 5b, 6b of the ball bearings 5, 6 are abutted against the ends of the small diameter portion 17 so that the ball bearings 5, 6 can be positioned at the time of setting the ball bearings. It may be noted that a motor using a space ring, which is a separate member, instead of the small diameter portion 17 is also applicable although not shown in the drawings.
A base plate 15 is arranged on the bottom of the bracket portion 3 of the frame 1. A terminal of the coil 11 of each phase wound around the salient poles of the stator core 10 is taken out and connected to this base plate 15. When the coil 11 is energized through conduction to the base plate 15 from an external source, the stator core 10 and the drive magnet 8 repulse from each other to rotate the hub 7 and hence the disk D as a result of the rotation of the hub 7.
The thus constructed disk drive motor uses two ball bearings 5, 6, upper and lower, that rotatably support the hub 7. These ball bearings 5, 6 are arranged so as to be distanced from each other to improve the rigidity of the motor through an improved rotational characteristic. As a result, a space 16 is present between the upper and lower ball bearings 5, 6, the space 16 being surrounded by the inner circumferential surface of the small diameter portion 17 of the hub 7 and the outer circumferential surface of the center shaft 2.
In the thus constructed disk drive motor, the seal members 5c, 6c are arranged for the ball bearings 5, 6, respectively, to prevent dust produced within the respective ball bearings from leaking outside the ball bearings using these seal members 5c, 6c. Further, since the first seal means 14 and the second seal means 24 are provided along the way to the space 19 outside the motor from the ball bearings 5, 6, almost all the dust can be checked from leaking out into the space 19 outside the motor. According to the magnetic fluid seal mechanism such as the seal means 14, in particular, there is no gap which would allow air to pass between the rotating member and the fixed member, which in turn prevents the leaking of dust completely.
However, in the case of forming a seal mechanism by a small gap such as the second seal means 24, the inner space of the motor is not completely closed, allowing fine dust particles to be mixed with the air present in such gap and thereby leaking the dust particles to the outside space 19 through the gap.
Further, in the seal members 5c, 6c arranged on the respective ball bearings 5, 6, tiny gaps allowing the air to pass therethrough are present with respect to the inner rings of the ball bearings. Therefore, dust within the ball bearings may, in some cases, leak out.
Such leakage of dust is encouraged by the flow of air within the motor produced by the rotation of the hub 7. In the case of the conventional disk drive motor as shown in FIG. 3, in particular, the large space 16 is present between the ball bearings 5, 6. This space 16 allows a flow of air to be produced in the entire part of the motor including this space 16 and causes dust produced by the ball bearings 5, 6 to ride on the flow to reach a space 18, thereby disadvantageously allowing the dust to leak out into the outside space 19 through the second seal means 24, although only slightly. The dust that has leaked out into the space 19 outside the motor deposits on the signal reading means such as the disk D and the magnetic head and thereby subjects the disk drive apparatus to inconvenience.